This invention relates to injection molding and more particularly to an injection molding system with at least one heated probe which is actuated between open and closed positions to valve gate the flow of pressurized melt to the cavity.
Valve gating is, of course, well known in the art. However, this normally involves actuating a valve pin which is mounted centrally in a heated nozzle to control the flow of melt through the gate. An example of this type of hydraulically actuated valve pin is disclosed in the applicant's Canadian Pat. No. 1,177,213 which issued Nov. 6, 1984. While some of these valve pins are driven in both directions, some of these previous systems just drive the valve pin to the closed position and rely on injection melt pressure to return the pin to the open position. Examples of this are shown in the applicant's U.S. Pat. No. 4,013,393 which issued Mar. 22, 1977 and Japanese Patent Application Laid Open No. 55-61438 to Tokuhara which was published May 9, 1980.
Similarly, it is well known to have injection molding systems with a heated probe mounted in a fixed position in a well in the cavity plate around which the melt flows to the gate. An example of this is shown in the applicant's U.S. Pat. No. 4,376,244 which issued Mar. 8, 1983. More recently, the applicant's U.S. patent application Ser. No. 537,054 filed Sept. 29, 1983 now U.S. Pat. No. 4,576,567 and continuation-in-part application Ser. No. 680,286 filed Dec. 10, 1984 now U.S. Pat. No. 4,611,394 disclose probes having external melt channels or grooves extending longitudinally.
While fixed probes are entirely satisfactory for many applications, for some difficult to mold materials it is desirable to use valve gating. However, valve gating has had the disadvantage that the valve pin is not heated, which can result in problems with the valve pin tip seating improperly in the gate due to melt solidification in the area.